SLM4110

The inductor value for SLM4110 buck LED driver is calculated based on ripple current requirements: L = (Vout × (Vin - Vout)) / (Vin × fsw × ΔIL), where Vout is LED forward voltage × number of LEDs, Vin is input voltage, fsw is switching frequency (typically 1MHz for SLM4110), and ΔIL is inductor ripple current (typically 30% of LED current). For example, driving 3 LEDs (Vf=3V each, Vout=9V) from 24V input at 700mA: L = (9 × (24-9)) / (24 × 1MHz × 0.21) = 26.8μH. Standard value 27μH or 33μH can be used. Higher inductance reduces ripple but increases size. Lower inductance allows smaller size but increases ripple and may affect current regulation.

Use 33μH for most applications; contact FAE for specific calculations.

Recommended PCB layout practices for SLM4110: (1) Input capacitor - place ceramic capacitor (10μF) close to Vin and GND pins to minimize input ripple. (2) Inductor - keep inductor close to SW pin with short, wide traces. Use shielded inductor for low EMI. (3) Output capacitor - place close to LED cathode and GND for clean output current. (4) Current sense resistor - use Kelvin connection with separate traces for sense pins. Keep away from switching nodes. (5) Thermal management - provide copper area on PCB for heat dissipation, especially for high current applications. (6) Dimming input - keep dimming signal traces away from switching nodes to prevent interference. (7) GND connection - use single-point ground connection to prevent ground bounce.

Follow Silan's reference design layout for best performance and EMI.

PWM dimming with SLM4110: (1) Connect PWM signal to DIM pin. The IC supports PWM frequencies from 100Hz to 20kHz. (2) Recommended PWM frequency is 1kHz - high enough to avoid visible flicker, low enough for good dimming linearity. (3) Duty cycle 0-100% controls brightness proportionally. 100% duty = full brightness, 0% = off. (4) For analog dimming, apply 0.5-2.5V DC voltage to DIM pin instead of PWM. (5) Dimming range - SLM4110 supports 1000:1 dimming ratio at 1kHz PWM. (6) For smooth dimming, use 12-bit or higher resolution PWM from microcontroller. (7) If PWM signal has slow rise/fall times, add 1nF capacitor from DIM to GND for noise filtering. Avoid frequencies below 100Hz to prevent visible flicker.

Use 1kHz PWM frequency for best balance of flicker-free operation and dimming range.

The SLM4110 includes comprehensive protection features: (1) LED open protection - if LED string opens, IC limits output voltage to prevent damage. (2) LED short protection - detects shorted LEDs and limits current. (3) Overcurrent protection - cycle-by-cycle current limiting protects against output shorts. (4) Thermal regulation - reduces LED current if die temperature exceeds threshold (typically 150°C). (5) Undervoltage lockout - disables operation if input voltage drops below 4V. (6) Thermal shutdown - shuts down if temperature exceeds 170°C, auto-restarts when cooled. These protections ensure safe operation under fault conditions and extend system lifetime. The thermal regulation feature is particularly useful - it prevents thermal runaway by automatically reducing current at high temperatures.

All protections are built-in; no external components needed for basic protection.

The SLM4110 is designed for single LED string operation. For multiple LED strings: (1) Parallel strings - not recommended due to current sharing issues. LEDs have varying forward voltages, causing uneven current distribution. (2) Series strings - can drive LEDs in series up to (Vin - 2V) / Vf. For 24V input and 3V LEDs, maximum is about 7 LEDs. (3) Multiple drivers - use one SLM4110 per string for best current matching. Sync PWM dimming signals for uniform brightness. (4) Current balancing - if parallel operation is necessary, use ballast resistors (inefficient) or active current balancing circuits. (5) Multi-channel drivers - consider Silan's SLM4130 for 3-channel applications with built-in current matching. For RGB applications, use three separate drivers or a dedicated RGB LED driver.

Use separate SLM4110 per string; consider multi-channel drivers for RGB applications.

SLM4110 efficiency depends on operating conditions: (1) Typical efficiency - 90-95% for most operating points. (2) Input voltage - higher efficiency at lower input voltages (less voltage drop across internal MOSFET). (3) LED voltage - efficiency = Vled / Vin × ηdriver. For 9V LEDs from 24V input, maximum theoretical efficiency is 9/24 = 37.5% before driver losses. (4) Current - efficiency peaks at mid-range currents (300-800mA). (5) Inductor - use low DCR inductor (<100mΩ) for best efficiency. (6) Example: 24V input, 3 LEDs (9V), 700mA: measured efficiency ~92%. Power loss = 9V × 0.7A × (1/0.92 - 1) = 0.55W. For high-efficiency applications, minimize difference between input and LED voltages.

Design for Vin close to Vled for best efficiency; expect 90-95% typical.